Reuse is the key value proposition of an SOA. Being able to share business logic with ease by the virtue of publishing and consuming a Web service can greatly benefit an organization. But one has to realize that it is incorrect to expect SOA to meet all software reuse needs. Performance overhead of a distributed call over the network will always be a detriment to consuming a lot of fine-grained distributed functions, even with the exponential rise of network bandwidth and computing capacity. Many real-life business transactions are complex and thus require complex processing logic. Spreading this business logic over multiple service providers will undoubtedly affect performance. Consumers nowadays require instantaneous response to their requests, so businesses can’t hide the inefficiency of their architectures behind batch processes running once a day. All this means that Web services can only expose coarse-grained functions so that a number of distributed calls are kept under control. So if an application is only interested in a very discreet piece of a reusable business logic, it may not be available as part of SOA.

Reuse of UI components is another example where SOA does not have an answer. This problem can be addressed to some extent by portals. In most instances, however, it is easier to share a library of UI components among multiple applications.

In some sense, SOA was borne out of inability to achieve reuse at the library/binary level (including binary wire protocol level, such as IIOP) as it became clear that most large organizations will always run on heterogeneous infrastructures with bits and pieces supplied by multiple vendors. But I think that hype and enthusiasm created by SOA (look, our Microsoft and IBM applications can finally share some services!) somehow made everybody forget about good old library and component reuse. Granted, library reuse can only work for a given technology/platform, however, in most organizations number of these platforms is limited to very few (e.g., JEE, .NET, mainframe), so the benefits could still be substantial.

I have a feeling that SOA somehow slowed down the evolution of general purpose component management and dependency management tools as many vendors decided to focus almost exclusively on Web services. The idea of a registry/repository is very applicable to any unit of reuse, not just to a Web service. Most SOA implementation efforts put Web services registry/repository in the center of SOA, however very few organizations (as far as I know) implement general purpose component repository as a centerpiece of their development process. The repository products have been around for some time (Flashline, logidex) but their use does not seem to be very wide-spread in development organizations. Maven is becoming a de-facto standard in the Java world but its use is still pretty rare on large projects where "roll your own" is still the norm. I'm also not aware of a similar tool for .NET and other languages or of an open source or inexpensive tool that could handle component management for multiple platforms.

There is also lack of standardization. SOA suffers from overabundance of standards and specifications. Situation with component-level reuse is quite different. RAS is just too complex; MOF is geared toward modeling and MDA. SCA can be applied generically to binary components as well as to Web services, but component management is simply not in its scope.

I just hope that vendors and their customers will sooner or later realize that SOA by itself is not the goal - better business and IT efficiency (and hence better ROI) provided by software reuse is. This goal can't be accomplished with "one size fits all" approach to software reuse.

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